Multiunit offshore platform

ABSTRACT

The invention relates to an offshore platform for use in relatively deep water, being equipped for exploratory purposes and/or for producing crude oil from a subsurface wellhead. The platform comprises a floatable hull section that detachably engages an intermediary jacket. The latter supportedly rests on or near the floor of a body of water and incorporates a removable wellhead structure. After use of the platform for drilling and completion operations at a well site, the jacket and wellhead structure are separated whereby the latter will remain at the site, while the jacket is removed by the hull for further use. The jacket is then raised from the ocean floor by the floatable hull for transfer to another well site.

United States Patent Ivo C. Pogonowski Houston, Tex. 809,820

Mar. 24, 1969 Mar. 23, 1971 Texaco Inc.

New York, N.Y.

Inventor Appl. No. Filed Patented Assignee MULTIUNIT OFFSHORE PLATFORM[56] References Cited UNITED STATES PATENTS 3,201,945 8/1965 Sutton6l/46.5 3,433,024 3/ I969 Diamond et 6l/46.5

Primary Examiner-Jacob Shapiro Attorneys-K. E. Kavanagh and Thomas H.Whaley ABSTRACT: The invention relates to an offshore platform for usein relatively deep water, being equipped for exploratory purposes and/orfor producing crude oil from a subsurface wellhead. The platformcomprises a floatable hull section that detachably engages anintermediary jacket. The latter supportedly rests on or near the floorof a body of water and incorporates a removable wellhead structure.After use of the platform for drilling and completion operations at awell site, the jacket and wellhead structure are separated whereby thelatter will remain at the site, while the jacket is removed by the hullfor further use. The jacket is then raised from the ocean floor by thefloatable hull for transfer to another well site.

' PATENTEU ma SHEET 20F 2 MULTIUNIT OFFSHORE PLATFORM The presentefforts toward exploration for, and production of crude oil and gassources, have gravitated to increasingly deeper offshore locations. Muchof the developing petroleum technology therefore has been directed tothe improvement of, and further advancement of concepts towardfacilitating economical removal of the crude product from deep waterwells. Generally, such offshore wells are developed utilizing eitherfixedly anchored platforms, or floating barges, the latter being ineffect movably restrained at the waters surface.

In the instance of rigidly anchored platforms, the support structureextends from the ocean floor to a point above the waters surface, andthere positions the drilling platform. The latter normally holds aderrick and draw-works, together with the other ancillary equipmentcharacteristic of such offshore drill rigs.

Platforms adapted for offshore work are relatively expensive; inmany'instances they are known to exceed several million dollars merelyfor the building, transporting and locating of the platform at aparticular site. It can be appreciated then that the economics ofoffshore drilling activities become less favorable as the water depthincreases. This analogy is due not only. to the greater height of thesupport platform to maintain the working deck above the water surface,but also to the lack of specific technology which might be relied on inthe design of a safe, workable structure.

Since every attempt at finding a productive offshore location does notmeet with success, it is economically feasible to in most instancesdisconnect the platform for the ocean floor and transport the entireunit for use at another drillingsite. The process is thereaftercontinued whereby exploratory wells may be attempted or completed at anumber of sites, utilizing the same platform.

v The actual construction of extra large offshore structures for deepwater use suggests numerous problems, prompted mainly by the platformsoutlandish size. Notably, while the structure can be readily fabricatedon shore, or at a shipyard, the unit must eventually be moved to anoffshore working area either by barge or by'self-flotation. Barging hasbeen utilized to a large extent, but the capability of this mode oftransportation has limitations. Not the least of these limitations isthe difficulty in moving a large completed structure from the shore andonto a barge. For example, there is the inherent strain imposed on thestructure by virtue of one or more of the transporting barges beingsubjected to rocking and tilting in response to the wave action of thewater. Further, in the instance where the platform is floated from abuilding site to a working area, the water immediately offshore of thebuilding site must of necessity be quite deep. This latter condition israre except where the drydock or construction facility includes asection that has been artificially deepened, which circumstance usuallyrequires firming of the land bank immediately adjacent to the water.

Thus, the technique of constructing an offshore platform and floatingthe same to a working location, has by and large been contingent on thesize of the platform and more specifically on the depths of the water inwhich it will function. With increased water depth, as a matter of gooddesign practice the lower end or base of the platform support structuremust be made increasingly wider that the platform will maintain uprightstability under a variety of unfavorable natural conditions prevalent atthe drill site.

It is therefore one of the objects of the invention to provide amultiunit offshore platform adapted to be versatile and readilyseparable into individual components. A further object is to provide aplatform of the type described which is easily transferable for reuse atdifferent drilling locations. A still further object is to provide adetachably connected offshore platform adapted to be readily andfloatably transported between points of operation. Another object is toprovide a separable type platform adapted to removably receive awellhead structure which is transported to a drilling site at which itremains after the platform itself has been removed to another site.Still another object is to provide a platform adapted for use in a deepwater location, which platform is characterized by a relativelywidespread base embodying a minimum amount of anchoring. And a stillfurther object is to provide an offshore platform adapted to utilize acentral anchoring section which functions, together with a relativelybroad base, to firmly position the platform at a drilling site.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIGS. 1, 2 and 3represent the sequential operations of an offshore unit of the typepresently contemplated showing a wellhead structure as used with thedrilling platform.

FIG. 4 is an enlarged view of the multiunit platform connected by aplurality of legs which join the surface positioned hull to the floorpositioned platform jacket.

FIG. 5 illustrates an embodiment of the jacket member normallypositioned at the floor of an under water site.

FIG. 6 is an enlarged segmentary view of a portion of the jacket andwellhead structure connection shown in FIG. 4.

In overcoming the foregoing structural problems and technologicaloperating difficulties, and to further advance the offshore petroleumdrilling techniques, the present invention discloses a novel offshoreplatform adapted principally to deep water use. The platform isfabricated of a multiplicity of detachably connected units including; afloatable hull, a controllably floatable well jacket, and a wellheadstructure. At least two elongated legs are operably connected toclamping means on the respective parts. Thus, the hull either supportsor is supported by the open frame jacket. The wellhead structure iscarried integral with the jacket during drilling and productionoperations, and is thereafter detached to permit removal of the jacketwhile leaving the wellhead structure firmly anchored in place.

Referring to the drawings, FIGS. 1, 2 and 3 illustrate a platform of thetype contemplated, in a sequence of situations including those in whichthe platform is floating, at the anchored position, and thereafterfurther floated without the wellhead structure. The latter is shownremaining in place at the under water wellhead. The platform includesfloatable deck section or hull H which is normally disposed at theplatform uppermost end. Well jacket J depends from the lower side ofbull H, the spacial relationship between the two being adjustablymaintained by at least two rigid, elongated legs 15 and I5. Wellheadstructure S is incorporated into the framework of jacket .I, beingremovable to pennit the structure S to be anchored by piling or the likedriven into the ocean floor during a drilling operation and thereafterseparated from jacket J as the latter is floated to the surface forreuse.

Referring to FIG. 4, hull section H includes an upper deck 11 forming atop working surface. A lower deck 12 spaced from deck 11 defines astorage and flotation section 13, the two decks being normally enclosedand partitioned by steel plate to form watertight compartments. Therespective decks are generally formed of steel plates welded into a unitto define a peripheral enclosure. Hull H is provided with an open well14 preferably at the bull's center although not limited to suchlocation. Well 14 forms an opening to accommodate drill string tools andother equipment supported by derrick l6 and lowered through the well tothe ocean floor.

Hull H as shown, is constructed in a triangular configuration to bestmeet the conditions requisite for floatability and seagoing stability.The geometric shape however is understandably not an absoluterequirement to the present invention but is rather exemplary. Eachcorner of hull H is provided with a leg elevating and locking clampshown as l7, l8 and I9 respectively. Each clamp further includessuitable mechanism such as a rack and pinidn mechanism adapted forelevating, lowering or locking the leg at a desired disposition.

Hull H is shown in FIG. 4 supported above the ocean floor and elevatedbeyond the water surface by rigid although adjustable linking meanswhich operably connects the bull to the jacket such as legs 15, and 15".The leg applicable to the present supporting function in the multiunitplatform might assume a number of embodiments. For example, the legs maybe of a general elongated tubular disposition formed of end weldedtubular short sections. The legs as a matter of practicality, may befabricated to a predesired length prior to assembling with the platformclamps. Alternately, and more usually, the legs are lengthened duringassembly with the hull as the latter supportably lowers jacket J to ananchoring position at the ocean bottom. Also within the purview of theleg structure applicable to the present application is the frequentlyused triangular sectioned leg formed of an open work structure.

Jacket J includes basically a welded, open framework of steel tubularmembers including a lower end into which wellhead structure S isincorporated in such manner to permit the latter to be readily removed.A horizontal base section is formed of terminally connected tubularmembers 22, 23 and 24. An enlarged plate assembly extending between, andperipherally connected to the respective base sections may be utilizedby the jacket as a template which functions as a broad bearing memberfor jacket J.

Jacket J further includes a plurality of upstanding leg guides 26, 27and 28 having a flared, frustroconical cap at the upper end adapted toreceive and direct the lower end of a support leg stabbed into theguide. Stabbing is normally accomplished by lowering the tubular leg inan upright attitude from the hull H, and manipulating the same toregister and fasten within a corresponding leg guide for raising thejacket from its anchored spot. With the leg, as for example 15,restrained at its upper end at clamp 17, and with the lower end fastenedinto leg guide 26, hull H and jacket J are fixedly disposed with respectto each other. The leg 15 lower end is firmly clamped within leg guide26 preferably by a contracting jaw arrangement, actuated from thesurface. However, cementing to form a rigid collar between theconcentrically disposed leg and guide may also be utilized, whichoperation will necessitate destroying at least part of the leg when itis removed from a guide.

Jacket J further includes a plurality of downwardly extending pileguides 29, spaced about the jacket and formed to receive one or morepiles 20. The latter in the usual manner, extend from the pile guidelower end and are imbedded into the ocean substratum to a predetermineddepth determined to be suitable for rigidly stabilizing the platform.

A central upright section of jacket J is formed of structural guidemembers oriented to define an elongated docking facility or cavity. Saidfacility comprises essentially a guide passage having an enlargedforward opening at the jacket lower end, and extending upwardly to aheight commensurate with the height of wellhead structure S. The lower,or forward opening of the docking cavity is adapted to slidably registerwith and retain a wellhead structure S during the period when the jacketis being transported or lowered into place in contemplation of adrilling operation. Further, when structure S is anchored, it slidablyguides a jacket J into place as the latter is lowered prior tocommencing a rework or similar operation on a functioning well.

Referring to FIG. 4, one embodiment of the docking facility includes twoor more collars 36 and 37 spaced longitudinally apart and being of across-sectional dimension in accordance with the outer dimensions of thewellhead structure. The respective collars are positioned in the jacketby lateral members 43 and 44 which radiate from, and are connected tothe jacket outer elements.

Wellhead structure 8 as shown in FIG. 4, includes a three leggedupstanding pylonlike arrangement which is fixedly positioned at theocean floor by a plurality of leg piles 25. The height of wellheadstructure S is best determined in accordance with the height of thewater in which the platform is operating. The structure will normallyposition the usual wellhead flow control equipment 10 to feet above theocean floor.

Structure S includes a generally triangular formed base comprised ofperipheral elements 51, 52 and 53. Upstanding comer posts 54 and 56extend from the respective comers of the base, are tapered inwardly to aconstricted upper end, and are joined at an upper neck piece 57. Eachcorner post is provided along its outer surface with a track or slidesurface extending the length thereof to facilitate sliding engagement ofthe wellhead structure with the jacket docking cavity.

Operationally, wellhead structure S is incorporated into the center ofjacket J. The respective comer posts 56 and 57 are adapted to closelyfit within the longitudinally spaced rubbing collars 36 and 37 whereby,in fully seated position, the collars will closely fit about thewellhead structure corner posts. To minimize the relative movementbetween the said members, remotely operated clamping or locking jaws areincorporated into one or both joined members. The locking or engagingmembers are remotely operable by use of hydraulic lines and ancillaryequipment, which, although not presently shown in detail, extend from anactuating mechanism on hull H.

An example of a clamping mechanism usable to achieve the releasablefeature of the invention is shown in FIG. 6 and includes a set of jaws25' depending inwardly from rubbing collar 36, and a second set of saidjaws 30 depending from the lower positioned rubbing collar 37. Saidupper and lower jaws respectively are incorporated within the dockingfacility and positioned to engage an upright member 56 of the wellheadstructure S. Said clamping jaws are communicated through hydrauliccontrol lines 40 and 45 with a form of hydraulic actuating means atthe'waters surface whereby the jaws can be remotely regulated to engageor disengage with the wellhead structure.

Each corner post 56 and 57 of the wellhead structure is provided withone or more piles 25 which pass through the post and extend from thebottom end thereof to be firmly and permanently imbedded into thesubstratum. The function of the piles, as in generally known, is tofixedly implant wellhead structure S in the ocean floor and toconcurrently hold jacket J at its ocean floor position.

Referring to FIG. 5, an alternate embodiment of the novel compositejacket and removable wellhead structure, is illustrated and includes theouter jacket section formed essentially of upstanding corner posts 61,62 and 63 together with the lower base forming elements 64, 66 and 67.Intermediate, albeit necessary structural elements have been eliminatedfrom the drawing and description to best illustrate the position andarrangement of the shown docking facility as incorporated into thejacket structure.

Said docking facility includes a plurality, and preferably two,concentrically disposed and longitudinally spaced circular guide rings68 and 69. Bracing members such as 71, 72 and 73 are connected to therespective rings to supportably position the latter with respect to eachother and to the jacket. The main structure guide rings as shown,include the upper positioned smaller ring 68, and the larger diameterlower ring 69 so dimensioned to readily receive a wellhead structurewhen the latter is at a subsea location.

As also shown in FIG. 5, for tall offshore platforms the jacket may beprovided with a relatively broad base to assure vertical stability.Toward this end, outrigger members such as 76 and 77 extend downwardlyfrom the jacket upper corners, and terminate in a plane with the jacketbase. Horizontal and vertical braces 79, 81 and 82 reinforce the mainoutrigger assembly 76 against bending under excessive platform loadingdue to lateral movement swaying or the like. In this form of jacketstructure, the sole anchoring facility is embodied into the dockingunit. Thus, the latter includes a plurality of pile guides 83, 84 and 86which extend from, and are terminally positioned by spaced guide rings68 and 69. The guides serve to retain piles which are driven into theocean floor for positioning the jacket. By concentrating the piledsection at or near the center of the jacket, and by providing arelatively wide base on the jacket, the amount of piling required isgreatly minimized. Further the time and cost expended in piling theplatform to the ocean bottom is substantially decreased. V

Referring again to FIG. 4, operationally, the present multiunit offshoreplatform is adapted for fabrication at one or more shore locations in'the form of discrete and separable members. Afier being fullyfabricated, the respective hull, jacket, wellhead structure and linkinglegs are normally of such a size as to prohibit ease of assembly,-andlaunching at or close to shore. Thus each individual unit isseparat elyfloated by barge or self-flotation to an offshore water depth where'theplatform might be conveniently assembled.

The assembly area is normally in relatively shallow water, having anocean bottom adaptedto support the jacket and wellhead structure withoutsinking into the substratum. With the hull floating on the, water'ssurface, the jacket and wellhead structure are controllably submerged byjudicious use of buoyancy tanks or similar means incorporated into thejacket structure. This practice of controlled submergence is of coursefamiliar in the art and not considered novel.

Hull H is deployed immediately above the jacket and aligned to positionthe respective leg clamps 17, 18 and 19 above the corresponding jacketleg guides 26, 27 and 28. Legs 15, and 15" are individually passed intothe corner clamps, lowered into the water, and lengthened by addition ofshort tubing length as needed. Fastening of the leg lower end to thejacket is achieved by clamping or cementing as herein mentioned, toprovide a rigid connection.

With the two or more legs thus connecting the floating hull with thejacket, the legs are drawn up to the hull by' jacks at the respectivecorner clamps whereby to raise the jacket above the ocean floor. Theentire support of the jacket is not necessarily relegated to thefloating hull, but may be supplemented by the buoyancy capabilities ofthe jacket structure itself. With the composite unit now being supportedby the floating hull, and by 'the partially buoyant jacket, the entireunit is towed to a water depth, or site at which it is to be used.

- Jacket J is again lowered by lengthening the respective corner legsthrough addition of leg'lengths, until the jacket lower end rests on theocean bottom. Anchoring of the platform in the usual manner is achievedby implanting piles which have been prepositioned in the pile guidesdisposed about either the wellhead structure and/or the jacket. Thepiling operation as mentioned is limited only to the wellhead structurein the instance where the base of the jacket is sufficiently widened byuse of outrigger elements.

Drilling and completion of the well is now achieved in the usual manner.Whether or not the well site is productive will usually determine thedisposition of the platform. In the event the well is completed and is aproducer or capped as a reserve source, the wellhead structure will bekept in place while the jacket is removed.

The latter is achieved by lowering hull H to a floating position andthen shattering the piles holding the jacket in place at the mud line.Where such piles are utilized in the instance where the wellheadstructure is the sole anchoring member, the connectors joining thejacket and the wellhead structure might be exploded or actuated, therebypermitting the jacket to be lifted. This is done by retracting the legsupwardlythrough the floating hull jacks and clamps, until the lowersurface of the jacket clears the top of the wellhead structure. in suchcondition the floating hull is again supporting the submerged jacketwhich might now be safely carried or transported to the shallow waterassembly location to be lowered onto and engaged with new replacementwellhead structures.

The, platform is now in readiness to be again towed to a drilling sitewith the new wellhead structure and whereby the jacket might again belowered and the previously mentioned procedure followed for the drillingand completion operation.

Other modifications and variations of the invention as hereinbefore setforth may be made without departing from the spirit and scope thereof,and only such limitations should be imposed as arev indicated in theappended claims.

lclaim: l. A multiunlt well drilling platform adapted for fixedpositioning at an offshore location in a body of water, said platformincluding: 1

a. a floatable hull;

b. a jacket normally disposed beneath said hull and having a foundationat the lower end thereof adapted for resting on the floor of said bodyof water,to function as a base for said drilling platform;

c. a wellhead structure removably connected to and carried by saidjacket for mounting fluid control equipment connected to a subsurfacewell, and including means for anchoring said structure to said floor;

d. adjustable linking means operably connecting said floating hull tosaid jacket whereby said hull, when floating at the waters surface, willsuspend said jacket above said floor, and when said jacket is positionedat said floor, said adjustable linking means will supportably maintainsaid hull above the waters surface;

e. said wellhead structure being separable from said jacket to remainaffixed to said floor when separated from said jacket; and

f. said jacket including a vertically aligned docking facility adaptedto slidably register with and connect to said wellhead structure.

2. In a drilling platform as defined in claim 1 wherein, said jacketdocking facility includes a plurality of docking guide members disposedtherein and vertically oriented to slidably register with and releasablyengage said wellhead structure when said jacket is lowered onto saidstructure.

3. In a drilling platform as defined in claim 1 wherein, said jacketincludes remotely actuated clamping means adapted to releasably engagesaid wellhead structure when the latter is re-- gistered in said jacketdocking facility.

4. in a drilling platform as defined in claim 1 wherein, said wellheadstructure includes pile guide means depending therefrom, and at leastone pile positioned in said pile guide means for imbedment into saidfloor'to anchor said structure.

5. In a drilling platform as defined in claim 1 wherein, said wellheadstructure anchor means includes a plurality of upstanding cylindricalpile guides having at least one pile carried therein whereby, the lattermay be imbedded into said floor and fastened into said pile guide toanchor said wellhead structure.

'6. In a drilling platform as defined in claim 1 including peripherallyspaced upstanding track members disposed longitudinally of said wellheadstructure toslidably engage said jacket docking facility when saidjacket is lowered through the water and onto said wellhead structure.

1. A multiunit well drilling platform adapted for fixed positioning atan offshore location in a body of water, said platform including: a. afloatable hull; b. a jacket normally disposed beneath said hull andhaving a foundation at the lower end thereof adapted for resting on thefloor of said body of water, to function as a base for said drillingplatform; c. a wellhead structure removably connected to and carried bysaid jacket for mounting fluid control equipment connected to asubsurface well, and including means for anchoring said structure tosaid floor; d. adjustable linking means operably connecting saidfloating hull to said jacket whereby said hull, when floating at thewater''s surface, will suspend said jacket above said floor, and whensaid jacket is positioned at said floor, said adjustable linking meanswill supportably maintain said hull above the water''s surface; e. saidwellhead structure being separable from said jacket to remain affixed tosaid floor when separated from said jacket; and f. said jacket includinga vertically aligned docking facility adapted to slidably register withand connect to said wellhead structure.
 2. In a drilling platform asdefined in claim 1 wherein, said jacket docking facility includes aplurality of docking guide members disposed therein and verticallyoriented to slidably register with and releasably engage said wellheadstructure when said jacket is lowered onto said structure.
 3. In adrilling platform as defined in claim 1 wherein, said jacket includesremotely actuated clampIng means adapted to releasably engage saidwellhead structure when the latter is registered in said jacket dockingfacility.
 4. In a drilling platform as defined in claim 1 wherein, saidwellhead structure includes pile guide means depending therefrom, and atleast one pile positioned in said pile guide means for imbedment intosaid floor to anchor said structure.
 5. In a drilling platform asdefined in claim 1 wherein, said wellhead structure anchor meansincludes a plurality of upstanding cylindrical pile guides having atleast one pile carried therein whereby, the latter may be imbedded intosaid floor and fastened into said pile guide to anchor said wellheadstructure.
 6. In a drilling platform as defined in claim 1 includingperipherally spaced upstanding track members disposed longitudinally ofsaid wellhead structure to slidably engage said jacket docking facilitywhen said jacket is lowered through the water and onto said wellheadstructure.